As shown in FIG. 1, a typical conventional membrane separation device is provided with a filtering membrane unit 3 which is disposed by way of being submerged in raw liquid pooled in a raw liquid processing tank. The conventional filtering membrane unit 3 incorporates a plurality of filtration membrane cartridges 5 inside of an upper casing 4 by vertically aligning them in parallel with each other at predetermined intervals. In addition, a gas supply unit 7 is disposed inside of a lower casing 6 in order to feed gas such as oxygen, air, or nitrogen gas, to raw liquid in accordance with specific uses. Each of the filtration membrane cartridges 5 stored in the filtering membrane unit 3 is internally provided with a permeated-liquid passage connected to a routed tube 9 of a suction tube 8 for sucking permeated liquid, where an end of the suction tube 8 is linked with a suction pump 10.
While operating the conventional membrane separation device 1, the suction pump 10 generates negative pressure against all the filtration membrane cartridges 5 stored in the filtering membrane unit 3 in order that permeated liquid can properly be sucked. On the other hand, gas such as oxygen or air (designated by arrowed mark A) is supplied to the gas supply unit 7 from an external source to enable the gas supply unit 7 to jet out a bubble flow into the space between adjoining filtration membrane cartridges 5 in the upward direction from the bottom of the filtering-membrane unit 3. The upward flow of bubbles generate an aerial lifting action to cause tangential flow along the membrane surface, said tangential flow sweeping away deposits on the membrane surface.
Conventionally, each filtration membrane cartridge 5 stored in the membrane separation device 1 is inserted in a gutter provided inside of each slit plate vertically set in the upper casing 4. However, since each filtration membrane cartridge 5 and the inner surface of each gutter remain in contact with each other over a substantial surface area, friction is generated between both surfaces, requiring the operator to carefully and smoothly move each of the cartridges 5 into and from the gutter.
Normally, any conventional filtration membrane cartridge 5 is based on the structure in which an organic filtering membrane is secured onto the surface of a plane rectangular membrane-supporting plate by bonding peripheral domains of the organic filtering membrane to the membrane-supporting plate. On the other hand, when securing the filtering membrane to the membrane-supporting plate with an adhesive agent, the adhesive strength is variable according to strength, durability, and chemical resistance properties of the selected adhesive agent, and therefore, the filtering membrane may incidentally be stripped off from the membrane-supporting plate.